Polygon-forming of round tube end - uses mandrel with taper and polygonal sections to first widen then shape by drawing

摘要

The arrangement is intended for shaping the end of a round- section tube (1) to form a tube end portion with polygonal cross-section. The end is first widened out (10) and a mandrel (6) with a corresponding polygonal portion (9) inserted, after which a die (5) with polygonal passage is drawn over the tube from the narrow end, or the tube together with mandrel drawn through the die. The extremity of the tube end may be further widened out (11) beyond the diameter of the polygonal portion. The diameter of the widened (10) round portion may be equal to or slightly greater than that of the circle circumscribing the polygon. Widening out and polygon forming may be carried out with a single mandrel.